1. Field of the Invention
The present invention generally relates to a coating composition having good coating properties and that is capable of forming a coating film which is excellent in film hardness, processing property, pollution resistance and acid resistance. More particularly, the present invention relates to a coating composition suitable for precoated steel plates used in the manufacture of vessels, and/or coated metal plates prepared with the composition of the present invention.
2. Description of the Related Art
Heretofore, as topcoating compositions for precoated steel plates used in the manufacture of vessels, coating compositions have often been used that are obtained by blending a mixture of a polyester resin (a basic resin) and a methyl etherified methylol melamine resin (a cross-linking agent) with a curing catalyst. This is typically because such coating compositions possess an excellent balance between hardness and processing property. Processing property generally refers to the durability of the coating when subjected to pressing or bending processes. That is, a coating which does not crack or peel off under pressing or bending is said to have an excellent processing property.
With regard to conventional precoated steel plates used in the manufacture of the vessels, characteristics such as pollution resistance and acid resistance in addition to the hardness and the processing property have recently been regarded as important.
In conventional polyester resin-methyl etherified methylol melamine resin coating compositions, the pollution resistance of the coating film can generally be improved by increasing the amount of the methyl etherified methylol melamine resin, or by increasing the amount of the curing catalyst. However, such increases in resin and/or catalyst may cause the processing properties and, most particularly the acid resistance of the coating film may become noticeably deteriorated.